Introduce UnprocessableContentStatus cop

Author: tuxagon

changelog/add_unprocessable_content_status_cop.md

@@ -0,0 +1 @@
+* [#1520](https://github.com/rubocop/rubocop-rails/pull/1520): Add `Rails/UnprocessableContentStatus` cop ([@tuxagon][])

config/default.yml

@@ -1232,6 +1232,14 @@ Rails/UnknownEnv:
     - test
     - production
 
+Rails/UnprocessableContentStatus:
+  Description: 'Use `:unprocessable_content` instead of `:unprocessable_entity`.'
+  Enabled: pending
+  Severity: warning
+  VersionAdded: '<<next>>'
+  Include:
+    - '**/app/controllers/**/*.rb'
+
 Rails/UnusedIgnoredColumns:
   Description: 'Remove a column that does not exist from `ignored_columns`.'
   Enabled: false

lib/rubocop/cop/rails/unprocessable_content_status.rb

@@ -0,0 +1,82 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # Enforces the use of :unprocessable_content instead of :unprocessable_entity
+      # for HTTP status codes, as :unprocessable_entity is deprecated in Rack 3.1.
+      #
+      # @example
+      #   # bad
+      #   render json: { error: "Invalid data" }, status: :unprocessable_entity
+      #   head :unprocessable_entity
+      #
+      #   # good
+      #   render json: { error: "Invalid data" }, status: :unprocessable_content
+      #   head :unprocessable_content
+      #
+      class UnprocessableContentStatus < Base
+        extend AutoCorrector
+
+        MSG = 'Use `:unprocessable_content` instead of `:unprocessable_entity`. ' \
+              'The `:unprocessable_entity` status is deprecated.'
+
+        def_node_matcher :unprocessable_entity_symbol?, <<~PATTERN
+          (sym :unprocessable_entity)
+        PATTERN
+
+        def_node_matcher :status_argument?, <<~PATTERN
+          (pair (sym :status) (sym :unprocessable_entity))
+        PATTERN
+
+        def on_sym(node)
+          return unless rack_3_1_or_newer?
+
+          return unless unprocessable_entity_symbol?(node)
+          return if in_hash_key_context?(node)
+
+          return unless status_related_context?(node)
+
+          add_offense(node) do |corrector|
+            corrector.replace(node, ':unprocessable_content')
+          end
+        end
+
+        def on_pair(node)
+          return unless rack_3_1_or_newer?
+
+          status_argument?(node) do
+            add_offense(node.value) do |corrector|
+              corrector.replace(node.value, ':unprocessable_content')
+            end
+          end
+        end
+
+        private
+
+        def rack_3_1_or_newer?
+          Gem::Version.new(Rack::VERSION) >= Gem::Version.new('3.1.0')
+        rescue ArgumentError, NoMethodError
+          false
+        end
+
+        def in_hash_key_context?(node)
+          node.parent&.pair_type? && node.parent.key == node
+        end
+
+        def status_related_context?(node)
+          parent = node.parent
+          return false unless parent
+
+          if parent.send_type?
+            method_name = parent.method_name
+            return %i[head render redirect_to].include?(method_name)
+          end
+
+          # Variable assignment or ternary expression
+          %i[lvasgn if].include?(parent.type)
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -136,6 +136,7 @@
 require_relative 'rails/uniq_before_pluck'
 require_relative 'rails/unique_validation_without_index'
 require_relative 'rails/unknown_env'
+require_relative 'rails/unprocessable_content_status'
 require_relative 'rails/unused_ignored_columns'
 require_relative 'rails/unused_render_content'
 require_relative 'rails/validation'

spec/rubocop/cop/rails/unprocessable_content_status_spec.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::UnprocessableContentStatus, :config do
+  context 'when Rack is older than 3.1 or not available' do
+    before do
+      allow(cop).to receive(:rack_3_1_or_newer?).and_return(false)
+    end
+
+    it 'does nothing' do
+      expect_no_offenses(<<~RUBY)
+        render json: { error: 'Invalid data' }, status: :unprocessable_entity
+      RUBY
+    end
+  end
+
+  context 'when Rack is 3.1 or later' do
+    before do
+      allow(cop).to receive(:rack_3_1_or_newer?).and_return(true)
+    end
+
+    it 'registers an offense when using :unprocessable_entity in hash argument' do
+      expect_offense(<<~RUBY)
+        render json: { error: 'Invalid data' }, status: :unprocessable_entity
+                                                        ^^^^^^^^^^^^^^^^^^^^^ Use `:unprocessable_content` instead of `:unprocessable_entity`. The `:unprocessable_entity` status is deprecated.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        render json: { error: 'Invalid data' }, status: :unprocessable_content
+      RUBY
+    end
+
+    it 'registers an offense when using :unprocessable_entity in head' do
+      expect_offense(<<~RUBY)
+        head :unprocessable_entity
+             ^^^^^^^^^^^^^^^^^^^^^ Use `:unprocessable_content` instead of `:unprocessable_entity`. The `:unprocessable_entity` status is deprecated.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        head :unprocessable_content
+      RUBY
+    end
+
+    it 'registers an offense when using :unprocessable_entity in ternary expression' do
+      expect_offense(<<~RUBY)
+        render json: { error: 'Invalid data' }, status: :unprocessable_entity ? :unprocessable_content : :ok
+                                                        ^^^^^^^^^^^^^^^^^^^^^ Use `:unprocessable_content` instead of `:unprocessable_entity`. The `:unprocessable_entity` status is deprecated.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        render json: { error: 'Invalid data' }, status: :unprocessable_content ? :unprocessable_content : :ok
+      RUBY
+    end
+
+    it 'does not register an offense when using :unprocessable_content' do
+      expect_no_offenses(<<~RUBY)
+        render json: { error: 'Invalid data' }, status: :unprocessable_content
+      RUBY
+    end
+
+    it 'does not register an offense when using :unprocessable_entity in hash key' do
+      expect_no_offenses(<<~RUBY)
+        { unprocessable_entity: 'Invalid data' }
+      RUBY
+    end
+  end
+end